1. Field of the Invention
The invention relates to solid electrolytic capacitors and methods of manufacturing the same.
2. Description of Related Art
Amorphous niobium oxide has received much attention as a dielectric material for next generation high-capacity solid electrolytic capacitors since it has high insulation and a high dielectric constant of about 1.8 times compared with tantalum oxide, which is employed for conventional solid electrolytic capacitors.
In a related art, solid electrolytic capacitors with niobium oxide are often influenced by heat-treatment such as reflow soldering processes. The stability of capacitance is inferior compared with solid electrolytic capacitors that employ other dielectric materials such as tantalum oxide. An improvement in this respect is shown in Japanese Published Unexamined Application No. 11-329902 discloses a solid electrolytic capacitor which has a formed niobium nitride region in the niobium oxide, which is a dielectric.
FIG. 16 shows a sectional view of a representative structure of a conventional rectangular solid-shaped solid electrolytic capacitor. As shown in FIG. 16, a conventional solid electrolytic capacitor 200 has an anode 101, which includes a rectangular solid-shaped base body 101a made of a porous sintered body of niobium powder, and an anode lead 101c with one part buried in the base body 101a. 
Dielectric layer 102 is made of amorphous niobium oxide and formed by anodic oxidation on the anode 101 to cover the anode 101. The dielectric layer 102 has a niobium nitride region.
In addition, an electrolyte layer 103 made of polypyrrole is formed on the dielectric layer 102 to cover the dielectric layer 102. On the electrolyte layer 103, a cathode 104 is formed to cover the electrolyte layer 103. The cathode 104 has a first conductive layer 104a made of the carbon paste formed to cover the electrolyte layer 103, and a second conductive layer 104b made of the silver paste formed to cover the first conductive layer 104a. 
A conductive adhesive layer 105 is formed on the upper surface of the cathode 104, and a cathode terminal 6 is formed on the conductive adhesive layer 105. An anode lead 101c exposed from the base body 101a is connected to an anode terminal 107 by welding. In addition, a mold resin 108 is formed to cover the second conductive layer 104b, the cathode terminal 106 and the anode terminal 107 so as to expose cathode terminal 106 and an end of anode terminal 107. The solid electrolytic capacitor of related art 200 is composed as above.
As described above, since the niobium nitride region is formed in the dielectric layer 102, the conventional solid electrolytic capacitor 200 is somewhat resistant to heat-treatment process, such as reflow soldering processes. The capacity thus remains can be rather constant during these heat treatment processes.
However, a solid electrolytic capacitor that comprises the niobium oxide with a niobium nitride region as described above, is less resistant to heat treatment process. That is leakage current between the cathode and anode increases after heat-treatment process such as a reflow soldering process.